The present invention relates to an ion implantation apparatus and an ion implantation method used in fabrication processes of semiconductor devices.
For semiconductor devices typified by VLSI circuits, there are constant desires for much higher integration density and higher performance. In order to meet such desires, it is necessary to carry out the fabrication processes of semiconductor devices under optimal conditions. For this reason, the optimal conditions of each fabrication process were found out heretofore by preliminarily producing trial semiconductor devices under various conditions and evaluating characteristics of the trial semiconductor devices thus produced.
In the case of ion implantation processes among the semiconductor fabrication processes, it was ordinary practice to preliminarily carry out ion implantation under various conditions in order to find optimal conditions. Of course, since the ion implantation is carried out with ion implantation apparatus, the conditions of ion implantation substantially mean operation conditions of the ion implantation apparatus.
The ion implantation apparatus is basically comprised of an ion beam generator for generating ions and selecting desired ion species to form an ion beam thereof, and an ion implantation section for directing the ion beam from the ion beam generator toward a silicon wafer for process to implement ion implantation. A well-known ion implantation section is of a type consisting of a target chamber the interior of which is kept in vacuum, and a wafer support wheel located in this target chamber. The wafer support wheel consists of a swing shaft mounted in a swingable state in the target chamber, a hub mounted in a rotatable state at a distal end of the swing shaft, and a plurality of arms radially extending from the hub, each arm having a wafer holder for holding a silicon wafer at the distal end thereof. The wafer support wheel is arranged to rotate around the hub and swing in a plane perpendicular to the ion beam so that the entire surface of wafer is irradiated with the ion beam.
The conventional ion implantation apparatus as described above is operated so as to uniformly implant the ions over the entire wafer surface in a single ion implantation process. In other words, doses of a wafer processed by the conventional, ordinary ion implantation apparatus are almost uniform in the wafer surface. For this reason, for example, in order to evaluate a plurality of ion implantation conditions, it was necessary to prepare and process wafers in the number equal to at least the number of conditions.
However, all chips obtained from one wafer were not necessary for determining the conditions of ion implantation by evaluating device characteristics. Therefore, many chips were wasted. Particularly, as the size of wafers has been increasing in recent years, more chips have been wasted and the cost per wafer has been becoming higher. Accordingly, there arises the problem in the method of uniformly implanting the ions over the entire wafer surface.
In order to evaluate a plurality of ion implantation conditions by use of a single wafer, there was also a conventional idea of forming plural types of different dose areas on a single wafer. This method, however, required masking or the like, so as to increase the number of steps for ion implantation, thus increasing the cost.
An object of the present invention is to provide an ion implantation apparatus and an ion implantation method capable of forming plural types of dose areas on a single wafer by a single ion implantation process, without the need for masking or the like.
In order to accomplish the above object, an ion implantation apparatus according to the present invention comprises an ion beam generator for generating an ion beam; a wafer support wheel for supporting a wafer to be implanted, the wafer support wheel being rotatable for revolution of the wafer so that the ion beam from the ion beam generator scans an entire surface of the wafer; a first drive motor for rotating the wafer support wheel; a swing shaft for supporting the wafer support wheel; a second drive motor for swinging the swing shaft and the wafer support wheel, the second drive motor being able to be driven in forward and backward directions and being adjustable in velocity; and control means for controlling swing velocity of the wafer support wheel by rotating the second drive motor, based on either of a plurality of basic swing velocity modes preset so as to uniformly implant ions in the entire surface of the wafer, wherein the control means controls rotational velocity of the second drive motor so that either one basic swing velocity mode out of the plurality of basic swing velocity modes is switched to another basic swing velocity mode at a switch position arbitrarily selected in a swing range of the wafer support wheel, thereby forming a plurality of areas of different doses in the surface of the wafer.
The present invention of the above construction was invented based on the idea that the swing velocity of the wafer support wheel was able to be instantaneously and suddenly changed by using the motor capable of being driven in both forward and backward directions and adjustable in velocity, as the second drive motor for swinging the wafer support wheel. Thanks to the provision of the control means as described above, a certain basic swing velocity mode is switched to another basic swing velocity mode in the middle of the swinging operation of the wafer support wheel in the swing range, so as to instantaneously change the swing velocity of the wafer support wheel, whereby several different dose areas are formed on the wafer as a result. Consequently, plural types of dose areas can be formed with accuracy on a single wafer by a single ion implantation process, without the need for masking or the like.
In the ion implantation apparatus of the present invention, more specifically, the control means is preferably one comprising setting means for setting a control swing velocity mode in which either one basic swing velocity mode out of the plurality of basic swing velocity modes is switched to another basic swing velocity mode at the switch position selected, and drive control means for rotationally driving the second drive motor according to the control swing velocity mode set by the setting means.
In order to accomplish the above object, an ion implantation method of the present invention is a method using an ion implantation apparatus comprising an ion beam generator for generating an ion beam; a wafer support wheel for supporting a wafer to be implanted, the wafer support wheel being rotatable for revolution of the wafer so that the ion beam from the ion beam generator scans an entire surface of the wafer; a first drive motor for rotating the wafer support wheel; a swing shaft for supporting the wafer support wheel; and a second drive motor for swinging the wafer support wheel and the swing shaft according to a basic swing velocity mode preset so as to uniformly implant ions in the entire surface of the wafer, the second drive motor being able to be driven in forward and backward directions and being adjustable in velocity, wherein during ion implantation, rotational velocity of the second drive motor is adjusted so that a basic swing velocity mode is switched to another basic swing velocity mode of a different dose at a switch position arbitrarily selected in a swing range of the wafer support wheel, thereby forming a plurality of different areas of different doses in the surface of the wafer.
This permits plural types of dose areas to be formed on a single wafer by a single ion implantation process, without the need for masking or the like, as described above.